1. Field of the Invention
The present invention relates to a portable memory device and, more particularly, to an IC card with anti-ESD (Electrostatic Discharge) means.
2. Description of the Related Art
FIG. 3 is a side sectional view of a conventional portable memory device, for example, an IC card. The IC card 1 has a connector 2 engaged with a terminal device (not illustrated) at one end of the IC card 1. Conductive outer panels 4 with interior surfaces coated with an insulating material 3 are provided on the upper and lower surfaces of the IC card 1. The outer panels 4 are spaced apart by an IC card frame 5 at predetermined interval. A substrate 6 which includes peripheral ICs 8 such as chip parts 7 and a memory IC is disposed in the IC card 1. The ground of the substrate 6 is connected to a lead 10 (a ground pin) of a ground terminal of the connector 2 through a ground line 9 and other electric circuits are connected to a connector pin 11. The conductive outer panels 4 have the same electric potential since these panels are electrically connected to each other through conductive members 12 placed between the panels, such as a plate spring, a coil spring and so on. The IC card 1 includes a battery 13 which is electrically connected to each part on the substrate 6 through a positive electrode terminal 14 and a negative electrode terminal 15.
Conventional IC card 1 has a configuration as described above. The IC card 1 is supplied with electricity from the terminal device (not illustrated) when it is inserted into the terminal device, and inputs and outputs data. When the IC card 1 is withdrawn from the terminal device after the data has been written in it, the IC card 1 is supplied with electricity from the battery 13 and retains data even if the memory IC is a volatile memory IC. If the memory IC is a non-volatile memory IC, supplying of electricity from the battery 13 is not required.
If the above mentioned IC is electrostatically charged when inserted into or withdrawn from the terminal device, there arises a large electric field (electric potential difference) between the conductive outer panel 4 and the wiring, the chip parts 7, the peripheral ICs 8 or other parts on the substrate 6. This large electric field may generate a static discharge between such parts and cause latch up of the peripheral ICs, including the memory IC or change in data caused by a malfunction of the memory IC and the like.